ITU-R (International Telecommunication Union Radio communication sector) is in progress with standardization of IMT (International Mobile Telecommunication)-Advanced which is a next-generation mobile communication system standard after third generation communication systems. IMT-Advanced aims to support IP (Internet Protocol)-based multimedia services that may provide a data rate up to 1 Gbps in stationary or low-speed moving situations and a data rate up to 100 Mbps while moving at high speed.
3GPP (3rd Generation Partnership Project) prepares for LTE-Advanced that is an advancement of LTE (Long Term Evolution) based on OFDMA (Orthogonal Frequency Division Multiple Access)/SC-FDMA (Single Carrier-Frequency Division Multiple Access) transmission schemes as system standards satisfying IMT-Advanced. LTE-Advanced is a leading candidate for IMT-Advanced. As main technologies, LTE-Advanced includes relay station related technologies.
A relay station is a device that relays signals between a base station and a terminal and used to expand cell coverage for a radio communication system and to enhance throughput of the system.
In an existing OFDM-based mobile communication system, a network has been configured so that a base station is directly connected to a terminal. However, in an advanced OFDM-based mobile communication system, a base station may be connected to a terminal via a relay station. That is, relay stations relay communication between base stations and terminals by transmitting transmission upstream or downstream transmission packets. This scheme is called “relaying”.
In a radio communication system including a relay station, a link between a base station and the relay station is referred to as a “backhaul link”. A link through which the base station transmits signals to the relay station is referred to as a “backhaul downlink”, and a link through which the relay station transmits signals to the base station is referred to as a “backhaul uplink”. There are various transmission modes that may apply to the backhaul downlink and the backhaul uplink. For example, such transmission modes include a single antenna transmission mode, which is a most basic transmission mode, a transmit diversity mode using a plurality of antennas, a rank 1 single codeword precoding transmission mode, a closed loop precoding based spatial multiplexing mode, and an open loop precoding based spatial multiplexing mode. Of such various transmission modes, any one or more transmission modes may be applicable to the backhaul downlink and/or backhaul uplink.
A control channel through which a base station transmits control information to a relay station is called “R-PDCCH (relay-physical downlink control channel)”, and a data channel through which the base station transmits data to the relay station is called “R-PDSCH (relay physical downlink shared channel). There is a problem as to how to configure a transmission mode for R-PDCCH and R-PDSCH that are transmitted on the subframe in the backhaul downlink. There is also a problem as to how to configure reference signals that apply to decoding for each of various transmission modes.